Thought you might find this interesting - this is my hull where I have the transducer for my Koden sounder embedded in a blob of silicone inside- it would appear that Micron Optima isn't ultrasonicproof :laugh:
No hole - the 'white' is the gelshield under the black optima, which in turn is under the blue optima. And yes, it is caused by the pings. I'm not exactly sure which model of transducer it is, but it's 120khz for sure, and 1Kw RMS I think. It's certainly powerful, it tracks the bottom of the hurd deep down to 150m when I go across it at 25 knots, and it doesn't even point straight down!